New micro-sensors to sniff out explosives

Washington: Researchers have discovered a way to detect explosives based on the physical properties of their vapours and are readying the

technology, which utilises micro-sensors, for field testing. "Certain classes of explosives have unique thermal characteristics that help to identify explosive vapours in presence of other vapours," said Thomas Thundat, Oak Ridge National Lab (ORNL) and University of Tennessee researcher who conducted the study with colleagues at ORNL and the Technical University of Denmark.

This technology is not only capable of detecting explosives in traces but also capable of distinguishing between explosive and non-explosive chemicals

, and differentiating between individual explosives such as TNT, PETN, and RDX, said an ORNL release. Thundat and others have been working on explosive sensors for years. Typical sensors use ion mobility spectrometers, which ionise tiny amounts of chemicals and measure how fast they move through an electric field.

While these instruments are fast, sensitive and reliable, they are also expensive and bulky, leading many researchers in the last few years to try to find a cheaper and more portable device for detecting explosives. Much of this research focuses on micromechanical devices - tiny sensors that have microscopic probes on which airborne chemical vapours deposit. When the right chemicals find the surface of the sensors, they induce tiny mechanical motions and those motions create electronic signals that can be measured.

These devices are relatively inexpensive to make and can sensitively detect explosives, but often have the drawback that they cannot discriminate between similar chemicals - the dangerous and the benign. They may detect a trace amount of TNT, for instance, but they may not be able to distinguish that from a trace amount of gasoline.

Seeking to make a better micromechanical sensor, Thundat and his colleagues realised they could detect explosives selectively and with extremely high sensitivity by building sensors that probed the thermal signatures of chemical vapours. These findings are described in the latest issue of Review of Scientific Instruments, published by the American Institute of Physics (AIP).